Electric sound reproducer



July 12 1927.

A. A. THOMAS ELECTRIC SOUND REPRODUGER Filed March' 1926 INVENTOR Patented July 12, 1927.

UNITED srarss ADOLPH A. THOMAS, OF NEW YORK, N. Y.

ELEGTRIG sotmn-nnrnonucnn.

Application filed March 1 5', 1926. Serial No. 94,676.

My invention relates to the art of repro- I ducing sound by electrical means, and 1138' object is to provide a sound reproducer capable of giving a richer, fuller and more nearly natural tone reproduction than is possible to obtain with prior devices. At the present time m loudspeaker type, although it is not limited to this articular field.

Brie y stated, the reproducer of my invention embodies two diaphragms actuated out of phase with each other .by a predetermined amount, so that the sound waves produced by one diaphragm are like reflected or echoed waves of those produced by the other'diaphragm. The combined tonal efi'ect of this double reproduction is like hearing the original sound by the natural process of receiving not only the direct but also the I reflected sound waves.

' of the diaphragms.

. mitted' sound.

' It is my theory that the natural reproduction of sound must take into account not only the direct waves issuing from the source of sound, but also the reflected waves that are always present in sound propagation as we encounter it in ordinary life. True, broadcasting studios are so constructed that all reflection of sound waves is revented and only direct waves strike t e microphones. In my opinion that is all wrong, for it robs the transmitted sound of its'natural richness and quality. That is why prior loudspeakers cannot possibly give a natural reproduction of the original sound: they can reproduce only the direct waves that struck the microphone, thus giving a thin reproduction that lacks body. 4

Right here is where my invention comes to the rescue. By means of two diaphragms operating out of predetermined phase wlth each 0t er, I supply the previously lacking reflecte or echoed waves which are necessary to impart naturalness to speech or music. Any suitable electromagnetic mechanism may be used to actuate the dia hragms. In the embodiment which I pro.-

' or at the present time as the best expression of my idea, I employ a pair of independent coils for controlling the operation These coils are connectedin separate circuits through which flow electric im fiplses representing transe impulses in one circuit are de'phased with respect to the impulses new, instrument finds spe-- cial usefulness 1n telephone receivers of the.

in the other circuit, with the result that one of the dia hragms slightly lags behind the other diap iragm in thesame way that reflected or echoed sound waves la behind the direct waves. The amount of p ase displacement between the impulses in the two controlling circuits can be regulated for the best acoustic effect in each particular instance.

Since the basic idea of my invention may bepractlcally embodied b means of many different constructions, I 0 not consider it necessary to show or describe, in all me-- chanical details, any particular form of instrument. My invention will be fully understood from a descriptionof the diagrammatic views illustrated in the accompanying drawings, in which Fig. 1 representsdiagrammaticall aradio loudspeaker embodying the princip e of my invention; and

Fig. 2 shows a slightly modified form.

Referring first to Fig. 1, we have a pair of diaphragms A and B, which aresupposed to be properly constructed and mounted. Any practical electromagnetic mechanism may be emfployed to actuate each dia hragm. Bfy way. o eXample' I have indicated a pair 0 magnetic armatures L-and 2 pivoted centrally at 3 to vibrate between the pole pieces 4 and 5 of a pair of magnets (not shown); The magnets furnish a normally constant field. Each armature is connected to its associated diaphragm by a link or rod 6. Armatures 1 and 2 extend throu h fixed coils O and 0 respectively. Coil is connected in a circuit 7, which also includes a secondary coil S. Coil C is'connected in a circuit 8 having a secondary coil S and a choke coil 9. The secondary coils S and S are induotively associated with a primary coil P,

these three coils constituting a transformer indicated as a whole by T. The primary coil P is in the plate circuit 10 of a vacuum tube V of usual construction.v A battery 12 or other source of normally constant otential su plies the primary coil with a ow of norma 1y steady current, which has no efiect on the secondar coils S and 8*.

It will be un erstood that potential variations in the grid circuit 13 of the tube produce amplified current impulses throu h coil P, and these current impulses may e said to be an electric'representation or image of the transmitted sound waves. The ourrent fluctuations in coil P induce corresponding impulses in the secondary circuits of coils C and C However, the impulses in circuit 8 of coil C will lag behind the 1mpulses in secondary circuit 7 on account of the retarding effect of choke 9, as w1ll be clear to those familiar with this art. in other words, the impulses in secondary C11- cuits 7 and 8 are dephased with respect to each other, and the amount of this phase displacement (ceteris paribus) depends upon the self-inductance of choke coil 9, which is preferably adjustable as to its inductance value. Since the electric impulses passing throu h coil C lag behind those of coil C, the vi rations ofdiaphragm B will slightly lag behind those of diaphragm A. The amount of this lag is only a fraction of a second and should be just enough to represent the phase difierence between direct and reflected waves. This can readily be determined by experiment. When the phase displacement between the induced currents in coils C and G is properly adjusted, the combined tone effect of the diaphragms will result in a more natural reproduction than is possible to obtain with a single diaphragm or with several diaphragms reproducing only direct sound waves.

If desired, a condenser 14 may be included in secondary circuit 7 to advance the phase ofthe induced impulses with respect to those in circuit 8. Condenser 14 may be used in lieu of choke 9 or in addition thereto. @I'dinarily, however, one or the other of ary circuits 7 and 8 are fed with a normally constant current from batteries 15 and 16, respectively, and each circuit preferably includes a variable resistance 17 to control the normal flow of current. coils C and G are mounted on magnets or soft-iron cores 18, the polar ends of which terminate in o erative relation to the diaphragms A an B. These, of course, are of magnetic material in this-instance. Qtherwise, what has been said about Fig. 1 is fully applicable to Fig. 2 without the necessity of repetition. The diaphragms should preferably be 0 identical construction, so that one diaphragm is an echoing likeness (as it were) of the other. Although I. have spoken of only two diaphragms, it is clear that each diaphragm may be replaced by two or more diaphragms of difierent natural frequencies to encompass the entire musical scale. In

that case, the diaphragms of each set will operate in unison, but the diaphragms of one set will lag behind the other set, as (pie B.

viou'sly; explained for diaphragms A an Whatlclaim; as my invention is: 1. A sound reproducer having a pair of diaphragms, electromagnetic mechanism for The controlling 1,ess,seo

olperating each diaphragm independently of t e other, said mechanism being controlled by electric impulses representing transmitted sound, and means for so controlling said mechanism that said electric impulses cause said diaphragms to vibrate slightly out of unison.

2. A sound reproducer having a pair of diaphragms arranged to be operated independently of each other, an electromagnetic actuating device associated with each diaphragm, each of said devices including a coil, means for connecting said coils independently with a common, circuit of electric impulses representingtransmitted sound, and means for dephas-ing the impulses in one coil with respect to the impulses in the other coil, whereby the impulses in said circuit cause vibration of said diaphragnisin dephased relation.

Sound-reproducing apparatus comprising a primary circuit traversed by electric impulses representing transmitted sound, two independent secondary circuits operatively associated with said primary circuit, means for dephasing the induced'current impulses in one of the secondary circuits relatively to the impulses in the other secondary circuit, and an acoustic member controlled by the current impulses in each secondary circuit, so that said members vibrate in dephased relation.

4. Sound-reproducing apparatus comprising a primary circuit traversed by electric impulses representing transmitted sound, two independent secondary circuits opera- L vely associated with said primary circuit, means for dephasing the induced current impulses in one of the secondary circuits relatively to theimpulses in the other secondary circuit, an acoustic member controlled by the current impulses in each secondary circuit, so that said members vibrate in de phased relation, and means for re lating the amount of phase displacement etween the current impulses in the two secondary circuits.

E An electric sound reproducer havin a pan of diaphragms, means for vibratin said diaphragms in dephased relation, an

electric means for regulating the amount of phase displacement between said diaphragms.

o 6. In apparatus for electrically reproducingsound, the combination ofa circuit oi variableelectric impulses, a pair of substam tially identical di'aphragms, means controlled by. said impulses for simultaneously operating said diaphragms, and means for causin one of said diaphra 'ms to la 'sli htlv behind theother. a g a l 7. In the art of electrically reproducing sound, the improvement which consists in operating one diaphragm to represent direct sound waves and simultaneously operating ill!) a second diaphragm in lagging phase relaiaphrag'm to represent re cuit, repro ucing said impulses in two secondary circuits, displacing the phases of the induced currents in the secondary circuits relatively to each other a predetermined amount, and causing the dephased impulses to operate apair of diaphragms.

9. A sound reproducer having a pair of diaphragms arranged to be operated indecoil, means. for connecting said coils independently wlth a commonclrcult of electric} impulses representin transmitted sound, means for dephaslng t e impulses 1n one 0011 with respect to the impulses in the other coil,

whereby the impulses in said circuit cause vibration of said diaphra ms in dephased relation, and means for adfi usting the amount of phase displacement between the electric impulses in the two coils.

ADOLPH A. THOMAS. 

